Apparatus for thermally recording character patterns

ABSTRACT

Apparatus is disclosed for recording light images by exposure of a photoconductor thereto to render charge carriers therein mobile, subjecting the mobile charge carriers to a high frequency magnetic field to thereby effect induction heating of the photoconductor where exposed, and utilizing the heat generated in the photoconductor to act on a contacting heat sensitive recording substance.

tilted States Patent [1 1 [111 3,838,431 Germer Sept. 24, 1974 [5 APPARATUS FOR THERMALLY 3,570,380 3/1971 Kaminstein 95/45 RECORDING CHARACTER PATTERNS 3,673,594 6/1972 Kazan 250/317 X 3,752,667 8/1973 DOnofrio. 346/76 R X [76] Inventor: llorst-Germer, Am Schwarzen Berge 38, 3300 Braunschweig, Germany Primary Examiner-Joseph W. Hartary Filed p 12 1973 Attorney, Agent, or Firm-Joseph R. Spalla [21] Appl. N0.: 350,389

[57] ABSTRACT [30] Foreign Application Priority Data K d 1 .df h b pparatus 1s 1sc ose orrecor mg 1g timages yex- Apr. 18, 1972 Germany 2218640 posure of a photoconductor thereto torender charge "[52] s U 346/76 R 96/1 E 250/316 carriers therein mobile, subjecting the mobile charge [51] m m 17/00 carriers to a high frequency magnetic field to thereby [58] w 4 P 74 effect induction heating of the photoconductor where 6 3 96/1 exposed, and utilizing the heat generated in the photov conductor to act on a contacting heat sensitive record- [56] References Cited mg Substance UNITED STATES PATENTS 1 8 Claims, 10 Drawing Figures 3,386,551 6/1968 DOnofrio 346/76 R X Pmmmsamma. 3. 393131 v sum 1 or 3 x x Fig-2 PATENTEDSEPZMHM sum 2 or a I /9/ Fig-3 APPARATUS FOR THERMALLY RECORDING CHARACTER PATTERNS The present invention relates to a device for recording written characters or the like, on at least one data carrier, by means of electromagnetic radiation which arbitrarily projects the pattern of the character, and by means of particles susceptible to influence by said radiation, which particles are responsible for the recording of the characters.

For example, a method of producing written characters which remain visible, on a data carrier, is already known, in which method, in dependence upon a beam of electromagnetic radiation, the ink particles provided for the representation of the written character on the data carrier, are supplied with an amount of energy such as to render said particles visible whilst the radiation is still acting upon them, and leave them behind in the form of the character concerned, on the data carmet.

To this end, it has been proposed that in order to carry out printing after the manner of a typewriter, the beam should project the characters, selected individually by an input device, in the direction of arbitrarily selectable printing positions in a row on the data carrier, and that the beam should act upon the ink particles used for recording, which particles are located upon the data carrier or on a special ink carrier, and/or on the holder for same, the beam yielding up a quantity of energy which chemically or physically modifies the ink particles, e.g., German Pat. Application No. 1436647.

Although good quality written characters can be produced on a data carrier in this manner, the currently available radiation sources of adequate radiation intensity, are expensive. In addition to this, there is the fact that the power supply currently required for the radiation source in order to generate the radiation energy, would be too expensive for application to commerical printers and typewriters.

Although methods and devices have been proposed which employ radiation sources producing lower radiation intensities, the data carrier must be processed after the action of the radiation upon it, in order to render the written characters visible.

Also known are so-called thermal printers which, in order to produce a printed result on for example thermographic paper, use 20 directly (electrically) heated grid elements which are arranged in the field of five rows and four columns, e.g., type EPN 2100 Texas instruments Corporation, PO. Box 5012, Dallas, Tex., USA. v

The disadvantage is that only a limited number of grid elements, at the current time no more than 50, can be accommodated and operated on the area required for a normal kind of typewriter. The kind of printed result obtainable in this fashion, although suitable for some purposes, is very far removed from the sharp print produced by conventional typewriters or printers. In order to achieve this latter kind of result, at least 200 grid elements would be required to cover the type area. With the kinds of thermal printers which it is currently possible to construct, numbers of this order cannot be obtained. In addition, there is the fact that the grid elements have to be driven and heated by electronic means, and this means an additional expense.

The object of the invention is to provide a device for recording written characters or the like on at least one data carrier, which device on the one hand requires a less intense radiation source and a less elaborate system of control for same, than in the case with the known and proposed methods or arrangements, and on the other hand records a better printed result than thermal printers, preferably a printed result which is in keeping with the sharp print received by a typewriter.

In accordance with the invention, this is achieved by means of a radiation-electrical transducer arranged in the path of radiation, and a power source cooperating therewith, e.g., a generator for supplying energy to the charge carriers liberated whenever radiation is incident upon the transducer, these charge carriers increasing the temperature in the irradiated zones of the transducer, yielding up heat to recording particles.

It is an advantage that by way of radiation source, an ordinary electric light bulb, a flash bulb or the like, of low radiation intensity, long service life and with a relatively simple power supply can be used. This can easily be combined with an arrangement for producing a beam and for example with known forms of keyboards.

In accordance with the invention, different arrangements can be used to generate a beam. In a manner known per se, in order to project character patterns, interchangeable templates can be used, which are either inserted intermittently into the beam or can be passed through it in a continuous fashion. Without fundamentally altering the fundamental principle of the invention, it is also possible, depending upon the characters chosen to employ guided and intensitymodulated beams.

The radiation-electrical transducer, normally a photoelectric device, can equally be designed to operate as an amplifier system. At the points encountered by the radiation, for example in a photoconducting substance, charge carriers are liberated which give rise to a selective increase in conductivity, in accordance with the particular character pattern. The generator which is functionally associated with the radiation-electrical transducer, influences the liberated charge carriers so that current fractions, i.e., eddy currents, are generated in the transducer and produce there a thermal pattern which, in the particular required areas of the data carrier' transfers to the recording particles. Accordingly, the transducer is provided with a time-modulated and- /or position-modulated optical signal, through radiation, and with electrical power from a power source, so

'that in accordance with the particular character pattern, the transducer yields up a heat pattern to the recording particles. The transducer is responsible for local modulation of a flow-field produced by the power source in accordance with optical information. In one example, the power source is a high frequency generator which supplies a field winding that generates a high frequency magnetic field. The high frequency generator can be continuously switched on.

In another example, there is a functional connection between a switch for the high frequency generator and a switch for the radiation source (and possibly an arrangement for generating the beam). Here, the high frequency generator is switched in in a desired timed relationship to the other elements.

The field winding for the high frequency magnetic field can surround the radiation-electrical transducer in ring-fashion.

The radiation-electrical transducer, in another embodiment, is arranged between the two electrodes of a voltage source. The voltage source in this example acts as a generator that passes current through the irradiated areas of the transducer thereby heating up the irradiated areas of the transducer. One of the electrodes is transparent vis-a-vis the excitatory radiation. The radiation-electrical transducer normally contains a photoconducting substance. This can be arranged upon a radiation-transmissive carrier. In order to improve the efficiency of the arrangement, the photoconducting substance can be functionally associated with a phosphorescent substance. This latter continues to produce light until the liberated charge carriers have been provided with sufficient energy by the power source and are able to reliably produce the desired thermal pattern.

It is an advantage if, in the eddy current version, the radiation-electrical transducer is subdivided into mutually independent elementary areas. In this way, it is possible when required to avoid the production of blurred thermal patterns.

The invention is furthermore characterized by a carrier for thermoplastic ink in contact with the transducer.

During printing, the radiation-electrical transducer, the thermoplastic ink and a recording sheet are in contact with one another. In one embodiment of the invention, the recording particles can also be arranged upon the data carrier.

Losses are minimized if the generator contains a ferromagnetic circuit for the high frequency magnetic field.

Other features and details of the invention will be apparent from the ensuring description of embodiments with reference to the drawing wherein.

FIG. 1 illustrates a schematic diagram of the device;

FIG. 2 illustrates a fragment of FIG. 1 on an enlarged scale;

FIG. 3 illustrates a modified radiation-electrical transducer;

FIG. 4 illustrates a graph;

FIG. 5 illustrates a further graph;

FIG. 6 illustrates a construction detail;

FIG. 7 illustrates a cross-section through a further radiation-electrical transducer;

FIG. 8 schematically indicates a detail of an example of the invention, in side elevation;

FIG. 9 illustrates the arrangement of FIG. 8 in plan; and

FIG. 10 illustrates a construction detail. I Referring now to the drawing wherein like reference characters designate like or corresponding parts through the several views there is shown in FIG. 1 a schematic illustration of a device in accordance with on embodiment of the invention including a data carrier 16 on which written characters or the like can be recorded according to electromagnetic radiation images. A radiation source 1 is provided which can be connected by a switch 3 to a voltage source 2. By way of a radiation source 1, a suitable electric lightbulb, a flash bulb or the like can be used. The electromagnetic radiation produced by it is incident upon an arrangement 4 which produces a so-callcd radiation path or beam. This arrangement 4 can. for example. contain templates which can be introduced intermittently to the radiation or passed continuously through it. The templates are shaped to accord with the characters and in each case profile the radiation to produce the radiation path or beam 6 corresponding to the characters selected. The selection, for example, of the templates of the arrangement 4, is effected here in functional relationship with the operation of the radiation source 1, through a number of switches 13 of which, for reasons of clarity, only one has been shown in the Figure. For example, the arrangement 4 can consist of known, mechanically and/or electromechanically or electrodynamically selectable templates upon the servo elements of which the switches 13 operate. The switches 13 as well as the switch 3 will conveniently take the form of electronic timer switches because the circuits of the radiation source 1 and the arrangement 4 must be so matched to one another that the radiation path or beam 6 is maintained in each case for the requisite interval of time. The switch 3 as well as the switching elements 13, can be operated in a manner known per se and therefore not illustrated here directly by the keyboard of a typewriter, by a punched tape or magnetic tape reader, or for that matter by the output equipment of a data-processing system.

Instead of templates, the arrangement 4 for producing a beam 6 can also include devices by means of which a beam generated by the radiation source 1 is guided and intensity-modulated in accordance with the nature of a character to be recorded. The corresponding processes and sequences are likewise triggered by the switch 13. In association with the present invention, the term radiation path or beam 6 is intended to indicate radiation profile in accordance with the desired character, or a correspondingly guided beam.

In the beam or radiation path 6 there is provided an optical system 5, indicated purely schematically by means of which an adaptation to the particular situation can be effected.

Behind the optical system 5, considered in the direction of the radiation, the beam 6 is incident upon a radiation-electrical transducer 7, explained in more detail hereinafter, which is normally arranged upon a carrier 8. The radiation-electrical transducer 7 is followed by a mobile carrier 14, schematically illustrated in the present example, for thermoplastic ink 15 which is in contact with the likewise mobile data carrier 16. Behind the printing position of the data carrier 16, a plate 18 can be provided as support or the like.

In the example of FIG. 1, arranged ring-fashion around the radiation-electrical transducer 7, there is a field winding 12 for a high frequency magnetic field, which winding is connected to a high frequency generator 9. This generator can be continuously switched on or, alternatively, may be connected to a voltage source 10 via a drive arrangement schematically represented over switch 11. The switch 11, too, can be designed as an electronic timer switch and be operated by the typewriter keyboard or by other input equipment.

In front of the printing position, a known type of preheating station 17 for the thermoplastic ink 15 is illustrated. By means of the preheating station 17 the particular desired plasticity on the part of the thermoplastic ink 15 can be developed prior to the recording operation.

To explain the processes which occur in accordance with the invention for recording characters on the data carrier 16 there is shown in FIG. 2 an enlarged fragmentary view of FIG. 1. Out of the radiation coming from the radiation source 1, the radiation path or beam 6 corresponding to the character is stencilled through an arrangement 4 illustrated in section as a template and is directed through the radiationtransmissive carrier 8 on the radiation-electrical transducer 7 which may, for example, be a photoconductive layer. In the irradiated areas, charge carriers 7a are liberated which selectively increase the conductivity of the photoconducting substance.

The high frequency magnetic field produced by the winding 12 influences the liberated charge carriers 7a so that eddy currents are produced in accordance with the character pattern. These eddy currents produce a thermal pattern in the photoconductive layer and this thermal pattemis transferred by direct contact to the carrier 14 carrying the thermoplastic ink 15. The thermoplastic ink 15 is softened in accordance with the pattern of the character so that recording particles 15a are released to the surface of the data carrier 16.

By suitable choice of the radiation-electrical transducer 7, by proper design of the radiation source l, and by corresponding design of the high frequency magnetic field, the result can be achieved that different characters are transferred with equal quality to the data carrier 16. During a printing operation, the photoconducting substance is in intimate contact with the carrier 14 for the thermoplastic ink 15, and this in turn touches the data carrier 16.

By means of the preheating station, the thermoplastic ink 15 in front of the printing position can be preheated to a threshold such that the thermal image of the radiation-electrical transducer 7 has only to produce a tiny additional amount of heating, sufficient for local selective attainment of the melting temperature and there fore for transmission of the recording particles 15a to the data carrier 16.

With intermittent selection of character templates in the arrangement 4 and a sequence of about 25 characters per second, the dwell time of a template in the radiation in order to produce a beam or radiation path is between and milliseconds. This is sufficient time, with a small economically viable high frequency generator 9, to produce an adequate temperature rise in the radiation-electrical transducer 7 for the softening of the thermoplastic ink 15.

In examples which have not been illustrated, the recording particles 15a can also be arranged upon the data carrier 16. In this case, they may comprise a material which changes color when subjected to the action of heat, in the manner well-known for example from thermal copiers.

In cases where the arrangement 4 for producing the beam 6 cooperates with a template arrangement moving continuously through the beam, at a character rate of 25 characters per second and with a total of 48 different characters, there are only about 10 to 20 milliseconds of irradiation time available, if the definition uncertainty of a character is not to exceed 0.1mm. In order, despite such short time intervals, to make available the power needed to melt the thermoplastic ink 15 without having. to use a high frequency generator 9 of a kind economically difficult to produce and capable of withstanding brief overloading, a preferred embodiment of the invention employs a radiation-electrical transducer 7 whose conductivity changes have a sufficiently long recovery time. As shown in FIG. 4, the conductivity K can remain, for example, for a period of t l l0ms above the conductivity k,, illustrated in broken line, which is sufficient to maintain a fully effective thermal pattern. In the diagram of FIG. 4, the value represents the duration of radiation incidence which is, for example, 4ms.

In order to still further improve this persistence of conductivity effect, the photoconductive layer of FIG. 3 can be functionally associated with a phosphorescent substance 19. As FIG. 3 shows, the phosphorescent substance 19 may take the form of a thin film which is arranged between the carrier 8 and the radiationelectrical transducer 7. In this manner, as those skilled in the art will appreciate, the conductivity decay characteristic can be influenced within wide limits. Instead of lining the radiation-electrical transducer 7 with the phosphorescent substance 19, in the manner shown in FIG. 3, it may also be possible to provide a chemical or technological compound of the phosphorescent substance with the photoconductive material of the trans ducer, and thus to ensure the requisite conductivity decay time. In FIG. 5, the combined action of photoconducting substance and phosphorescent substance has been qualitatively illustrated. The characteristic edge of the decay time corresponds to that shown in FIG. 4 and indicates the decay characteristic of the phosphorescent substance. The combined effect is indicated by curve c, whose behavior shows that the threshold conductivity k,, can be maintained for example up to t 20 ms.

In order to prevent differential eddy currents developed in areas which correspond to the different partial areas of the particular character to be recorded from developing non-uniform heating of the thermoplastic ink, the transducer can be subdivided into mutually independent elementary areas. As FIG. 6 shows, for this purpose, a radiation transmissive grid or grating 20 can be used which is either arranged directly over the transducer 7 or also, for example, directly on a template within the arrangement 4 used to produce the radiation path or beam 6. Through the meshes of the grid 20 on the radiation-electrical transducer 7, elementary areas 2ll are defined which are effectively isolated from one another. In this fashion, a pattern of liberated charge carriers 7a, on the lines of a checker arrangement, is produced in the radiation-electrical transducer 7.

Another possible way of subdividing the radiationelectrical transducer into mutually independent elementary areas is indicated in FIG. 7. A radiationelectrical transducer 7b contains a grainy, photoconductive substance for the purpose of subdivision. Through the graininess or granulation, once again, mutually independent areas are created.

FIGS. 8 and 9 illustrate in detail a schematic view of a possible design of the subject of the invention. The high frequency magnetic field excited by the field winding 12, is for the major part guided through a ferromagnetic core 22 provided with air gaps 23 and 24 for the passage of the carrier 14 carrying the thermoplastic ink 15, and of the data carrier 16. The ferromagnetic circuit 22 consists of the two arms 22a and 22b. The arm 22a contains an opening 220 for the passage of the radiation path or beam 6. Beneath the opening 22c, the radiation-electrical transducer 7, with its carrier 8, is

located. The field winding 12 is connected to the high frequency generator 9. The ferromagnetic core consists, preferably, of sintered magnetic material.

In the case where an arrangement corresponding to that of FIGS. 8 and 9 is applied to tape printers, the design of the ferromagnetic core 22 can, of course, readily be modified to exclude the air gap 23.

In a furtheembodiment of the invention, the power source which supplies the energy to the liberated charge carrier 7a, to heat the transducer 7 and thereby the thermoplastic ink 15, can operate without a magnetic field. In accordance with FIG. 10, although shown only schematically here, the radiation-electrical trans ducer 7 could also be arranged between two electrodes 25 and 26 of which heat 25 is radiation-transmissive in design. The two electrodes 25 and 26 are connected to a voltage source 27 which supplies, through the irradiated areas of the transducer 7, currents which heat the transducer 7 at the desired locations.

Without in any way modifying the essence of the invention, it is equally possibly for several of the illustrated devices for recording written characters or the like to be arranged adjacent one another or in any arbitrary combination.

By way of phosphorescent materials, for example, zinc-sulphide and cadmium-sulphide, activated with suitable heavy metal such as copper, silver, manganese, can be used.

Because the mechanisms of photo-conduction and phosphorescence are related, by way of photoconductive substances, advantageously selenium, copper suboxide, lead sulphide, zinc sulphide and cadmium sulphice, can be used.

The mutually independent elementary areas shown in FIG. 7, can, for example, be small equisized spheres of photoconducting substance which are sintered using a suitable heat resistant material. The small spheres of photoconducting substance can also be formed as a deposit in any suitable liquid which later solidifies. By way of insulating material, any solid material can be used which will withstand the temperatures developed and will pass at least the majority of the radiation. Particularly suitable in this context are gas, and in many cases, too, a silicon synthetic. Because of its good antifriction properties, a fluorated hydrocarbon, for example, Teflon, can be used.

I claim:

1. An apparatus for recording character patterns comprising:

a photoconductive layer;

means for exposing said photoconductive layer to an incident character light pattern;

means for directing a high frequency magnetic field through said exposed areas of said photoconductive layer during the life of the change of conductivity thereby to heat said photoconductive layer;

and means responsive to the heat generated in said photoconductive layer for recording said character pattern.

2. An apparatus as recited in claim 1,

said means responsive to generated heat in said photoconductive layer comprising particles incorporated in a record element.

3. An apparatus as recited in claim 1,

said means responsive to heat generated in said photoconductive layer comprising particles in a discrete layer and a record element in contact with said particles.

4. An apparatus as recited in claim 1,

said photoconductive layer including a phosphorescent material.

5. An apparatus as recited in claim 1,

said photoconductive layer comprising mutually independent elementary areas.

6. An apparatus as recited in claim 1, including a radiation transparent grid disposed in the path of the incident character light pattern.

7. An apparatus as recited in claim 1, further including means for preheating said means responsive to heat generated in said photoconductive layer.

8. Apparatus for recording type characters defined by light patterns comprising,

means for generating type character light patterns,

a layer of photoconfuctive material,

means for exposing said photoconductive layer to a generated character pattern to render charge carriers therein mobile,

a transfer element in heat transfer contact with said photoconductive layer,

said transfer element having a carrier and a transfer material coated thereon meltable in response to heat,

a record sheet in contact with said transfer material for receiving melted transfer material,

and means for directing high frequency magnetic flux lines through exposed areas of said photoconductive layer while charge carriers are mobile to oscil late said mobile charge carriers and generate heat in said photoconductive layer, said generated heat melting said transfer material whereby it transfers to said record sheet. 

1. An apparatus for recording character patterns comprising: a photoconductive layer; means for exposing said photoconductive layer to an incident character light pattern; means for directing a high fRequency magnetic field through said exposed areas of said photoconductive layer during the life of the change of conductivity thereby to heat said photoconductive layer; and means responsive to the heat generated in said photoconductive layer for recording said character pattern.
 2. An apparatus as recited in claim 1, said means responsive to generated heat in said photoconductive layer comprising particles incorporated in a record element.
 3. An apparatus as recited in claim 1, said means responsive to heat generated in said photoconductive layer comprising particles in a discrete layer and a record element in contact with said particles.
 4. An apparatus as recited in claim 1, said photoconductive layer including a phosphorescent material.
 5. An apparatus as recited in claim 1, said photoconductive layer comprising mutually independent elementary areas.
 6. An apparatus as recited in claim 1, including a radiation transparent grid disposed in the path of the incident character light pattern.
 7. An apparatus as recited in claim 1, further including means for preheating said means responsive to heat generated in said photoconductive layer.
 8. Apparatus for recording type characters defined by light patterns comprising, means for generating type character light patterns, a layer of photoconfuctive material, means for exposing said photoconductive layer to a generated character pattern to render charge carriers therein mobile, a transfer element in heat transfer contact with said photoconductive layer, said transfer element having a carrier and a transfer material coated thereon meltable in response to heat, a record sheet in contact with said transfer material for receiving melted transfer material, and means for directing high frequency magnetic flux lines through exposed areas of said photoconductive layer while charge carriers are mobile to oscillate said mobile charge carriers and generate heat in said photoconductive layer, said generated heat melting said transfer material whereby it transfers to said record sheet. 